The present invention relates to the manufacture of identification plates and the like having legible indicia thereon. More specifically, the invention involves a process and apparatus for the manufacture of such identification plates which have characters covered with retroreflecting material formed on the plate in an indented or recessed configuration.
Items of the type to which the present invention relates are usually formed by means of a compression die apparatus wherein self-adhesive retroreflective material shaped in the form of characters to be applied to an identification plate is positioned upon the male counterpart of the compression die apparatus with the adhesive side of the retroreflective material facing upwardly. The retroreflective characters are thus pasted to a plate blank or the like and they are compressed or indented thereinto in order to form recesses shaped as the characters. The present invention relates generally to a device for implementing and improving this process.
In the prior art, for example German OE-PS No. 319,066, there are known techniques whereby the application and indentation of characters into an identification plate may be performed in a single operation. Such methods generally tend to be economical from the point of view of the time which is involved but the product which is produced sometimes exhibits characteristics which are undesirable. For example, it occasionally occurs that individual characters become detached from the identification plate. It has been found, based upon experience in the manufacture of such plates, that the detachment of the letters or characters occurs primarily because of air bubbles which may be randomly formed between the applied characters and the surface of the plate itself during the manufacturing stage when the characters are adhered to the plate and the impression of the characters is made in the plate. Such air bubbles usually are difficult to remove even under the application of extremely high pressures. These air bubbles are of a high compression type and eventually lead to separation of the adhered character from the surface of the plate proper.
The present invention is aimed toward eliminating and overcoming drawbacks of this type in the manufacture of identification plates having recessed retroreflective characters.